1. Field of the Invention
The present invention is directed to a techniques for the installation of a payload in a remote location and, more particularly, to techniques involving the installation of a subsea payload using a surface support vessel and a remotely operated vehicle.
2. Description of the Background
A significant amount of effort has been expended during the past 20 years to further develop systems which will facilitate the economic recovery of hydrocarbon from offshore installations. Exemplary prior art offshore drilling and production technology, particularly with respect to "completing" a well to produce hydrocarbons, is disclosed in U.S. Pat. Nos. 3,516,489, 3,638,720, and 3,987,741. In a typical offshore wells is drilled from either a ship or an offshore platform. A separate subsea production facility may be installed after drilling. One type of subsea production installation utilizes hollow structural columns which are buoyed to impart a tensional force on the columns, as disclosed in U.S. Pat. No. 4,391,332. U.S. Pat. Nos. 4,673,313, 4,740,110, and 4,744,698 disclose prior art technology with respect to marine production risers, platform grouting techniques, and marine silos.
Convention techniques for the installation of subsea equipment, commonly referred to as a subsea payload, utilize a surface support vessel or ship, in conjunction with a remotely operated vehicle or ROV. Traditional installation techniques employ a ship with dynamic positioning devices which compensate for turbulence, heave, roll, pitch, and/or drift of the ship caused by surface or near surface conditions. Such dynamic positioning or compensation devices maintain the ship over the subsea installation site, and minimize the effects of vessel motion induced on the subsea payload during installation. Such compensation devices are, however, very expensive, and surface vessels with such compensation systems are of a very limited availability.
Most subsea payloads are installed with the assistance of an underwater ROV. A great deal of technology has been developed to increase the capability of ROVs, although ROVs themselves are very expensive. A garaged-type ROV is disclosed in U.S. Pat. No. 4,010,619. Smaller and less expensive "all electric" ROVs have also been used to assist in subsea payload installation, and the latter ROV typically is not provided with a subsea garage. U.S. Pat. No. 4,721,055 discloses a technique for increasing the payload capacity of an ROV by utilizing a "clump weight" in conjunction with conventional ROV buoyancy to increase the lifting capacity of the ROV. The ROV as disclosed in the '055 patent may be operated in a positive buoyancy mode, a free swimming mode, or a towed mode.
Various specialized techniques and systems have been devised to facilitate installation of a particular type of subsea payload. U.S. Pat. Nos. 4,484,838, 4,618,285, and 4,784,525 each disclose especially designed employment systems to address an installation problem for a substantially single purpose or a single type of payload. The '285 patent discloses the use of a gas or other buoyant material with in a centralizer body to allow a payload to be installed from below up to the subsea assembly, while most subsea payloads are lowered from above down to the subsea assembly. Each of these patents disclose techniques which are not economically practical for the installation of most subsea payloads. Accordingly, the cost of installing subsea payloads remains high. Surface vessels with compensation devices are frequently unavailable, and are extremely expensive and not justified for most payload installations. As a result, scheduling of the installation of a subsea payload is frequently delayed until periods when the sea conditions substantially minimize the movement of the surface vessel. Even under these conditions, however, substantial time is required to install the payload, and accordingly the ROV used in the installation technique itself is expensive, with a good deal of the difficulty and time being attributable to the minimal although ever-present movement of the ship.
The disadvantages of the prior art are overcome by the present invention, and improved subsea payload installation techniques and methods are hereinafter disclosed for substantially minimizing the difficulty and expense associated with installing a payload on a subsea assembly.